Asymmetry ratio as a parameter of Eu 3+ local environment in phosphors

Study of the local environment of certain ion is quite a complex problem. Due to the unique luminescent properties, Eu3+ ions can be used as a structural probe. In this paper, effect of doping concentration, excitation wavelength and excitation mechanism on asymmetry ratio was systematically studied using Y3Al5O12:Eu3+, YVO4:Eu3+ and Y2O3:Eu3+nanophosphors. The asymmetry ratio gives information about the local surrounding and environmental changes around the Eu3+ ions. Asymmetry ratios of YAG:Eu3+ and YVO4:Eu3+ nanopowders were calculated using standard technique and the obtained average values were found to be 0.75 and 8.2, respectively. However, it is found that standard method of asymmetry ratio calculation is suitable only for samples where all Eu3+ ions occupy one site. The “multisite model” of asymmetry ratio calculation was developed and used for Y2O3:Eu3+ nanocrystalline powders. Average value of asymmetry ratio for Eu3+ ions occupied “normal” sites is 6.0 and for Eu3+ ions occupied “defect” sites is 2.3.